The present invention relates to a system and method for ozone treatment of ballast water during transit of a vessel from one port to another.
A sea faring vessel routinely docks at a first port where it is loaded with a cargo that the vessel transports to a second port where the cargo is unloaded. The vessel then returns to the first port where it is loaded with another cargo. Typically, the vessel travels empty from the second port back to the first port to pick up another cargo. The vessel is equipped with ballast tanks that can be filled with water to maintain the balance of the vessel on an even keel when it travels empty. Conventional ballast tanks can include valves usually mounted over apertures through tank bulkheads. The valves are actuated to move water between and into and out of various ballast tanks to trim the vessel when empty of cargo or when carrying an unevenly distributed cargo.
The vessel fills its ballast tanks by taking on sea water, usually at its cargo discharge port. The sea water is charged into the ballast tanks at the same time that the vessel off loads its cargo. The vessel then travels to its cargo loading port where it takes on cargo while at the same time it empties at least some and typically all of its ballast tanks by discharging the ballast water into the loading port water environment.
The ballast water intake is below the water line of a vessel usually at or near the vessel hull bottom. The ballast water contains algae, zooplankton and other organisms that are indigenous to the cargo discharge port. Significant quantities of these indigenous organisms are loaded into the ballast tanks along with the water. The vessel then transports these organisms to a cargo loading port where the organisms are discharged into the water environment along with discharged ballast water. The organisms may not be indigenous to the water environment of the cargo loading port. Some of these organisms may be deleterious to and very much unwanted in the loading port environment. They cause damage to the water environment and replace benthic organisms and clear plankton communities that provide food and larvae for resident native species in overlying waters.
The zebra mussel (Dreissena polymorpha) is an example of an unwanted organism that has been spread by ballast water. The zebra mussel was first found in the mid eighteenth century in the northern Caspian Sea and in the Ural River. Since then the mussel has quickly spread to other parts of the world by means of ballast water discharge. The mussel has threadlike tentacles that enable the mussel to adhere to any vertical or horizontal surface. The mussel reproduces quickly and attaches to any hard underwater surface. It is particularly adherent to the shell of another mussel. Stacks of mussels can completely clog water intake orifices. In a short time, they reach population densities in excess of 30,000 mussels per square meter. Zebra mussels have been known to completely shut down municipal water treatment plants and industrial water systems.
The spread of the zebra mussel and other nonindigenous organisms is an immense problem. The mussel was found in the Great Lakes in late 1988. It is believed that it was carried to North America in the ballast of ships from Europe. It was first prevalent in Lake Erie. Since then, the mussel has spread into Lake Michigan and into rivers of the Midwest and Northeast.
In 1996, Congress passed the National Invasive Species Act (P. L. 104-332) to stem the spread of nonindigenous organisms by ballast water discharge. The act reauthorized the Great Lakes ballast management program and expanded applicability to vessels with ballast tanks. The Act requires the Secretary of Transportation to develop national guidelines to prevent the spread of organisms and their introduction into U.S. waters via ballast water of commercial vessels.
The Act establishes guidelines that require that vessels that enter U.S. waters after operating undertake ballast exchange in the high seas. In this method, a vessel empties its ballast on the high seas and refills the ballast tanks with sea water. However, the emptying of ballast tanks causes an imbalance that makes the exchange of ballast water exchange on the high seas both dangerous and sometimes impossible because of weather conditions. Additionally, high seas exchange requires manpower that many vessels do not have or cannot economically provide. There remains a need for an effective and economical ballast water treatment process to prevent the spread of nonindigenous organisms.